hmmmmmmm then try not assigning the values index by index, use initializing list and omit the array size as
double[] array = new double[] { 1, 2, 3, 4, 5, 6 };
For your case
double[] gAGA8Xj = new double[]{ Methane, Nitrogen, . . . ., Argon };
if it is index out of range exception, other two solutions are also right.